I use this
, the Nyko Xbox 360 Charge Base.
You can drop 2 controllers in (the charging contacts are on the back of the battery packs) and it acts as a stand for the controllers. Comes with 2 proprietary rechargable NiMH battery packs.
I got mine back in October 2006 and it still works fine with the battery packs that came with it. Charge time is pretty quick, but not as good as the very best rechargeable batteries. It's WAY more convenient though, you never have to open the battery packs or unplug/plug any cables. This is important for me as my Xbox 360 is in a closet in a separate room from my TV.